<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="bootstrap-4.5.0-dist/css/bootstrap.css">
    <style>
        .item{height:260px;}
        .item:nth-child(1){background-color: royalblue;}
        .item:nth-child(2){background-color: green;}
        .item:nth-child(3){background-color: blueviolet;}
        .item:nth-child(4){background-color: yellow;}
    </style>
</head>
<body>
    <!-- 12个模块
         <576  ≥576px   ≥768px     ≥992px     ≥ 1200
        .col-  .col-sm  .col-md   .col-lg     .col-xl-

    col-md-3    ≥768px    4个模块   25% 
    col-sm-6    ≥576px    2个模块   50% 
    col-12   ....         1个模块   100%

     -->
    <div class="container-fluid">
        <div class="row">
            <div class="item col-md-3 col-sm-6 col-12"></div>
            <div class="item col-md-3 col-sm-6 col-12"></div>
            <div class="item col-md-3 col-sm-6 col-12"></div>
            <div class="item col-md-3 col-sm-6 col-12"></div>
        </div>
    </div>
</body>
</html>